title: Hormonal induction of beta-casein gene expression: requirement of ongoing protein synthesis for transcription.
abstract: Hormonal induction of beta-casein gene expression was studied using a two-step culture of mouse mammary explants and RNA blotting analysis. The explants prepared from pregnant mice were cultured first for 4 days under nonlactogenic conditions to reduce the initial level of beta-casein transcripts and then induced to express beta-casein gene in the presence of insulin, hydrocortisone, and PRL for up to 3 days. Among the six different combination of hormones tested in the first incubation period, the combinations of insulin and epidermal growth factor was found to reduce the residual level of beta-casein transcripts in cultured explants to a nearly undetectable level and allow the highest induction in the second incubation period. The increase in beta-casein transcripts was detected as early as 30 min of induction with insulin, hydrocortisone, and PRL, and its level increased more than 100-fold over the initial level at 24 h. The increase in beta-casein transcripts was blocked by concomitant addition of the protein synthesis inhibitors cycloheximide or puromycin with the three hormones. Cycloheximide inhibited the increase in beta-casein gene transcription that was elicited by insulin, hydrocortisone, and PRL, but did not alter the stability of beta-casein transcripts. These results suggested that protein synthesis was required for hormonal activation of beta-casein gene transcription.
authors.affiliation: Laboratory of Molecular and Cellular Biology, National Institute of Diabetes, Digestive and Kidney Diseases, Bethesda, Maryland.
authors.forename: M
authors.initials: M
authors.lastname: Yoshimura
authors.forename: T
authors.initials: T
authors.lastname: Oka
mesh_terms: D000818:Animals; D002364:Caseins / Q000235:genetics*; D003513:Cycloheximide / Q000494:pharmacology; D004355:Drug Stability; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects*; D006728:Hormones / Q000494:pharmacology*; D051379:Mice; D008809:Mice, Inbred C3H; D009924:Organ Culture Techniques; D011247:Pregnancy; D014176:Protein Biosynthesis; D011506:Proteins / Q000037:antagonists & inhibitors / Q000235:genetics; D014158:Transcription, Genetic
chemical_list: D002364:Caseins; D006728:Hormones; D011506:Proteins; D003513:Cycloheximide